It is known to employ rotating rectifier assemblies in generators, such as high speed generators utilized in aircraft. The use of rotating rectifier assemblies permits the elimination of brushes which frequently require maintenance and/or replacement.
A typical brushless generator has three distinct generating systems, including a main generator, an exciter and a permanent magnet generator. The permanent magnet generator includes permanent magnets for establishing a magnetic field which is employed to induce a current field in a set of windings. This induced current is in turn employed to generate a magnetic field in the exciter; and this magnetic field in turn is employed to induce an even higher level of current, typically three phase alternating, which is then employed to generate a magnetic field for the main generator.
In order to avoid the use of brushes, it is necessary that the magnetic field and the main generator be in the rotor so that the output of the system can be taken from the stator of the main generator. To generate a suitable magnetic field in the rotor, it is necessary to utilize direct current, as opposed to alternating current. Since the output of the exciter is an alternating current, this current must rectified to direct current. A rectifier assembly is used for this purpose. In order to avoid resort to brushes, it is necessary that the rectifier assembly interconnecting the exciter and the main generator field winding be carried by the rotor of the generator. U.S. Pat. Nos. 4,570,094; 4,603,344 and 4,628,219 disclose examples of known rotating rectifier assemblies.
Rotating rectifier assemblies carried in a rotor of a generator are subjected to high centrifugal loading so that much care must be taken to assure that the components of the rectifier are adequately supported against such forces. For example, some rectifiers must be designed to withstand speeds as high as 30,000 rpm. The diode semiconductor devices used in the rectifier assemblies also dissipate power in the form heat during their use. Without proper attention to cooling, the diode semiconductor devices will fail. In the known rotating rectifier assemblies of the aforementioned U.S. patents, the diode semiconductor devices and other assembly components are compressed in a direction along the axis of rotation of the rectifier assembly for maintaining good electrical contact and for maintaining contact of the diode wafers with adjacent heat sinks, the cooling of the diode semiconductor devices being accomplished by circulation of a coolant in contact with the heat sinks.
In aircraft generating systems, in addition to the usual reliability concerns, size and weight restrictions are significant. The compactness, or lack thereof, of the rotor will dictate certain bearing and housing size selections, and thus affect the weight of the system. Since the rotating rectifier assembly forms part of the rotor and therefore influences its size, every effort is made to minimize its size and weight.
Disclosure Of Invention
An object of the present invention is to provide an improved rotating rectifier assembly and a method of making the same which overcome one or more of the aforementioned problems. More particularly, an object of the invention is to provide a new and improved rotating rectifier assembly which is highly reliable and of a relatively small size and weight.
A further object of the invention is to provide an improved rotating rectifier assembly wherein the diode semiconductor devices are adequately supported against high centrifugal loading which occurs during rotation of the rectifier assembly, while at the same time the diode semiconductor devices are relieved of compressive stresses on the other components of the rectifier assembly due to axial preloading of the assembly.
Another object of the invention is to provide an improved rectifier assembly and a method of making the same wherein effective, direct cooling of the diode semiconductor devices is accomplished to prevent premature failure of the devices.
These and other objects are obtained by the rotating rectifier assembly of the invention which comprises a plurality of components arranged along an axis of rotation of the assembly and means for forcing the components together in a direction along the axis, wherein means are provided for supporting at least one diode semiconductor device on at least one component of the assembly such that the axial force on the components from the means for forcing is not transmitted to the at least one diode semiconductor device. Relieving the compressive stresses on the diode semiconductor devices, particularly where the diode semiconductor devices are subjected to centrifugal loading during high speed rotation, reduces the likelihood of stressrelated failures of the diode semiconductor devices.
The improved rotating rectifier assembly of the invention is further characterized by the provision of means for flowing liquid coolant through the rectifier assembly in direct contact with the at least one diode semiconductor device for cooling the device. The rotating rectifier assembly acts as a centrifuge for the liquid coolant when it is rotating. It has been found that, because of the hydrodynamics during rotation, gas, normally air, is separated from the liquid coolant, typically oil, and centrifuged to the center of the rectifier assembly. This can reduce cooling efficiency by preventing liquid contact with surfaces to be cooled. The rectifier assembly of the invention avoids this problem by providing means located along the axis of rotation of the rectifier assembly for escape of the separated gas from the assembly.
In a disclosed, preferred form of the invention, the rotating rectifier assembly comprises a generally tubular housing; and at least one diode subassembly arranged within the housing, the subassembly including at least one diode semiconductor device, a support affixed to one side of the at least one semiconductor device and connector means affixed to an opposite side of the at least one semiconductor device. The at least one diode semiconductor device is preferably affixed to the support and the connector means by solder.
The support in the disclosed embodiment is in the form of a plate which extends transverse to the axis of rotation of the rectifier assembly. Means are provided for coupling the at least one diode subassembly for rotation with the housing of the assembly. In a disclosed form of the invention this means includes a tab on the support plate which is received within a cooperating groove on the interior of the housing. The rectifier assembly further comprises means for axially positioning the at least one diode subassembly in the housing without compressively loading the at least one semiconductor device. As a result of this arrangement, the at least one diode semiconductor device is firmly supported within the housing while not being compressed by an axial loading on the other components of the assembly.
Passage means are provided in the rectifier assembly for circulating a liquid coolant through the rectifier assembly for direct cooling of the at least one semiconductor device. As an additional feature of the invention, the support of the aforementioned at least one diode subassembly is provided with a hole therethrough on the axis of rotation of the rectifier assembly to allow escape of gas which is centrifugally separated from the liquid coolant during rotation of the rectifier assembly. An additional component of the rectifier assembly, a resistor in the disclosed embodiment, is located on the axis of rotation of the rectifier assembly within the assembly housing and adjacent the at least one diode subassembly At least one of the support and the additional component are provided with a radially directed slot formed therein in communication with the whole in the support The slot serves as a passageway for gas centrifugally separated from the liquid coolant to move to the hole in the support and escape the assembly.
The diode subassembly in the disclosed form of the invention comprises a plurality of diode semiconductor devices which are each located in one of a plurality of spaced locations on the support for rectifying respective phases of a multi-phase alternating current, specifically, three spaced locations are employed for rectifying a three-phase alternating current input to the rectifier assembly. Insulating means extend between the support and the connector means for physically and electrically separating the diode semiconductor devices of the respective spaced locations. The connector means comprise a plurality of thin connector plates associated with respective ones of the plurality of spaced locations. Electrical terminal means are provided on each of the connector plates for connecting respective electrical conductors to the connector plates for inputting respective phases of the alternating current to the diodes of the diode subassembly.
Further, according to the preferred embodiment, the rectifier assembly comprises a pair of the diode subassemblies which together form a full wave bridge rectifier for taking input, three phase alternating current and outputting direct current voltage. The pair of diode subassemblies are arranged within the housing of the rectifier assembly in spaced relation along the axis of rotation of the rectifier assembly by means of a separator located between the subassemblies. The connector means of each of the pair of subassemblies face one another in spaced relation. The connector means and the diode semiconductor devices of the subassemblies have spaces formed therein through which respective ends of the separator extend such that the separator ends abut the respective supports of the subassemblies for preventing compressive loading of the diode semiconductor devices while the components within the housing are axially locked. For this latter purpose the rotating rectifier assembly further includes means for resiliently biasing the pair of subassemblies toward one another and against the separator. The separator is formed of an insulating material and has a shape such that it also physically and electrically separates the diode semiconductor devices and portions of the connector means on each subassembly, in the respective spaced locations from one another. Means are also provided for preventing relative rotation of the separator and the subassemblies.
From the above discussion of the improved rotating rectifier assembly of the invention, it can be seen that the method of making a rotating rectifier assembly according to the invention comprises the steps of axially loading components of a rotating rectifier assembly which are arranged within a generally tubular housing of the rectifier assembly, while supporting diode semiconductor devices of the rotating rectifier assembly within the housing and in relation to the other components of the rectifier assembly so that the diode semiconductor devices are not compressed by the axial loading of the components, whereby compressive stresses on the diode semiconductor devices due to the axial loading of the components are avoided. Further, according to the method, liquid coolant is flowed through the rectifier assembly in direct contact with the diode semiconductor for cooling the devices. As an additional step of the method, gas which is centrifugally separated from the cooling liquid during rotation of the rectifier assembly is permitted to escape from the rectifier assembly through passage means located along the axis of the rectifier assembly.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings, which show, for purposes of illustration only, one preferred embodiment in accordance with the present invention.